US scientists achieve 'turning point' in fusion energy quest

Scientists are trying to recreate the fusion reaction used by the sun to create almost limitless energy.

NASA

Scientists in the United States say they have taken an important step on a decades-old quest to harness nuclear fusion to generate nearly inexhaustible energy.

For the first time, two nuclear fusion experiments succeeded in producing more energy than was used to trigger the reaction, the journal Nature reports.

The researchers at the Lawrence Livermore National Laboratory in California, led by physicist Omar Hurricane, described the achievement as important but said much more work is needed before fusion can become a viable energy source.

They noted that they did not produce self-heating nuclear fusion, known as ignition, that would be needed for any fusion power plant.

Researchers have faced daunting scientific and engineering challenges in trying to develop nuclear fusion - the process that powers stars including our sun - for use by humankind.

"Really, for the first time anywhere, we've got more energy out of this fuel than was put into the fuel. And that's quite unique," Mr Hurricane said.

"That's kind of a major turning point, in a lot of our minds.

"I think a lot of people are jazzed."

Still many years from fusion being a practical energy source

Unlike fossil fuels or the fission process in nuclear power plants, fusion offers the prospect of abundant energy without pollution, radioactive waste or greenhouse gases.

Unlike the current nuclear fission energy, that is derived from splitting atoms, fusion energy is produced by fusing atoms together.

Experts believe it will still be many years or decades before fusion can become a practical energy source.

"I wish I could put a date on it," Mr Hurricane said.

"But it really is [just] research. And, you know, although we're doing pretty good, we'd be lying to you if we told you a date."

Of the uncertain path ahead in fusion research, Mr Hurricane compared it to "climbing half way up a mountain, but the top of the mountain is hidden in clouds. You can't see it. You don't have a map".

The research was conducted at the laboratory's National Ignition Facility (NIF), which was completed in 2009.

Lasers zap tiny fuel capsule to fuse atom nuclei

The scientists used 192 laser beams to zap a tiny target containing a capsule, less than 2 millimetres in diameter, filled with fusion fuel consisting of a plasma of deuterium and tritium, which are two isotopes, or forms, of hydrogen.

The fuel was coated on the inside of the capsule in a frozen layer less than the width of a human hair.

At very high temperatures, the nucleus of the deuterium and the nucleus of the tritium fuse, a neutron and something known as an "alpha particle" emerge, and energy is released.

The experiments created conditions up to three times the density of the sun.

The fusion-energy yield was increased about tenfold from past experiments, in a series that started last May.

One of the experiments produced more than half of the so-called Lawson criteria needed to reach ignition, but only about one-one hundredth of the energy needed for ignition.